O-band Amp Characterization Measurement
This commit is contained in:
Silas Labor Zizou
327
Classes/05_Lab/OSA_Advantest.m
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327
Classes/05_Lab/OSA_Advantest.m
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classdef OSA_Advantest < handle
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% Advantest Q8384 Optical Spectrum Analyzer (GPIB)
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% User inputs in nanometers
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% EXAMPLE:
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% span_nm = 70;
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% lambda_c_nm = 1310;
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% osa = OSA_Advantest( ...
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% 'span_nm', span_nm, ...
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% 'lambda_c_nm', lambda_c_nm, ...
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% 'resolution_nm', 0.1, ...
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% 'sampling_points', 10001 );
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%
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% osa.configure();
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% [lambda_nm, psd_dBm] = osa.measure();
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% figure()
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% plot(lambda_nm,psd_dBm);
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properties (Access = public)
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span_nm double = 5
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resolution_nm double = 0.05
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lambda_c_nm double = 1550
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sampling_points double = 1001
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timeout_s double = 10
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lambda_nm
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psd_dBm
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end
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properties (Constant)
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valid_resolutions_nm = [0.01 0.02 0.05 0.10 0.20 0.50]
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valid_sampling_points = [101 201 501 1001 2001 5001 10001];
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end
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properties (Access = protected)
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visaAddress string = "GPIB0::3::INSTR"
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end
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methods
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function obj = OSA_Advantest(options)
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arguments
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options.visaAddress string = "GPIB0::3::INSTR"
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options.span_nm double = 5
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options.resolution_nm double = 0.05
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options.lambda_c_nm double = 1550
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options.sampling_points double = 1001
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options.timeout_s double = 10
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end
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fn = fieldnames(options);
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for k = 1:numel(fn)
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obj.(fn{k}) = options.(fn{k});
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end
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assert(ismember(obj.resolution_nm, obj.valid_resolutions_nm), ...
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'Invalid resolution. Allowed: 0.01 | 0.02 | 0.05 | 0.10 | 0.20 | 0.50 nm');
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assert(ismember(obj.sampling_points, obj.valid_sampling_points), ...
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'Invalid # of Samp. Points. Allowed: 101 201 501 1001 2001 5001 10001');
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v = obj.connect();
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writeline(v,"*IDN?");
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disp(readline(v));
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delete(v);
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end
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function configure(obj)
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assert(ismember(obj.resolution_nm, obj.valid_resolutions_nm), ...
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'Invalid resolution. Allowed: 0.01 | 0.02 | 0.05 | 0.10 | 0.20 | 0.50 nm');
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assert(ismember(obj.sampling_points, obj.valid_sampling_points), ...
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'Invalid # of Samp. Points. Allowed: 101 201 501 1001 2001 5001 10001');
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v = obj.connect();
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writeline(v,"FMT0,HED0,SDL0");
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writeline(v,"BUZ0");
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writeline(v,"QUI0");
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writeline(v, sprintf("RES %gnm", obj.resolution_nm));
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writeline(v, sprintf("SPT %g", obj.sampling_points));
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writeline(v, sprintf("CEN %gnm", obj.lambda_c_nm));
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writeline(v, sprintf("SPA %gnm", obj.span_nm));
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writeline(v,"SWE 0");
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delete(v);
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end
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function [osa_x_nm, osa_y_dBm] = measure(obj)
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v = obj.connect();
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writeline(v,"CSB");
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writeline(v,"MEA1");
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active = 1; cnt = 0;
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while active
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pause(1);
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writeline(v,"MEA?");
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active = str2double(readline(v));
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cnt = cnt + 1;
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if cnt > obj.timeout_s
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delete(v);
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error("OSA_Q8384:Timeout","Measurement timeout");
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end
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end
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writeline(v,"PKL");
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writeline(v,"ODN?");
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readline(v); % number of points (not strictly needed)
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writeline(v,"FMT0,HED0,SDL0");
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writeline(v,"OSD0"); % Y-axis
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osa_y_dBm = str2num(readline(v));
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writeline(v,"OSD1"); % X-axis
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osa_x_m = str2num(readline(v));
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osa_x_nm = osa_x_m.*1e9;
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delete(v);
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obj.lambda_nm=osa_x_nm;
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obj.psd_dBm=osa_y_dBm;
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end
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% --- Replace / extend plot() in OSA_Q8384 class ---
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function plot(obj, options)
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arguments
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obj
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options.FigureNumber double = 1
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options.Hold logical = true
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options.Title string = "OSA Spectrum"
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options.LineWidth double = 0.8
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options.Grid logical = true
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options.Color (1,3) double = [0 0.4470 0.7410]
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options.DisplayName string = ""
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end
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if isempty(obj.psd_dBm) || isempty(obj.lambda_nm)
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error('Record spectrum first: run osa.measure()');
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end
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fig = figure(options.FigureNumber);
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fig.Color = 'w';
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ax = gca;
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if ~options.Hold
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cla(ax);
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else
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hold(ax,'on');
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end
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plot(ax, obj.lambda_nm, obj.psd_dBm, ...
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'LineWidth', options.LineWidth, ...
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'Color', options.Color, ...
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'DisplayName', options.DisplayName);
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xlabel(ax,'Wavelength [nm]');
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ylabel(ax,'Optical Power [dBm]');
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if options.Title ~= ""
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title(ax, options.Title);
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end
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xlim(ax,[min(obj.lambda_nm) max(obj.lambda_nm)]);
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yl = ylim(ax);
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ylim(ax,[yl(1)-1 yl(2)+1]);
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if options.Grid
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grid(ax,'on');
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grid(ax,'minor');
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end
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set(ax, ...
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'FontSize',11, ...
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'LineWidth',1, ...
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'Box','on');
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if options.DisplayName ~= ""
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legend(ax,'show','Location','best');
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end
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end
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function osnr = computeOSNR(obj, options)
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% OSNR computation based on ratio method (RBW-independent)
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% Assumes obj.lambda_nm [nm], obj.psd_dBm [dBm/RBW] exist
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arguments
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obj
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options.bw_signal_nm double = 0.1 % channel bandwidth (0.1 for CW?!?!)
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options.ref_bw_nm double = 0.1 % OSNR reference bandwidth
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options.carrier_frequency = NaN;
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options.noise_guard_nm = 1;
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options.noise_window_nm =1;
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options.debugplots = 0;
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end
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assert(~isempty(obj.lambda_nm) && ~isempty(obj.psd_dBm), ...
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'Run measure() before computing OSNR');
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obj.lambda_nm = obj.lambda_nm;
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psd = obj.psd_dBm;
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% --- find carrier wavelength recorded in OSA ---
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% options.carrier_frequency [nm], options.noise_guard_nm, options.noise_window_nm
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if ~isnan(options.carrier_frequency)
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% local search window around expected CW carrier
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idx_search = obj.lambda_nm > (options.carrier_frequency - options.noise_guard_nm) & ...
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obj.lambda_nm < (options.carrier_frequency + options.noise_guard_nm);
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[~, imax_local] = max(psd(idx_search));
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lambda_search = obj.lambda_nm(idx_search);
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lambda_c = lambda_search(imax_local);
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[~,imax] = find(obj.lambda_nm==lambda_c);
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% define local noise windows directly adjacent to signal (guarded)
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idx_noise_left = obj.lambda_nm > (lambda_c - options.noise_guard_nm - options.noise_window_nm) & ...
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obj.lambda_nm < (lambda_c - options.noise_guard_nm);
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idx_noise_right = obj.lambda_nm > (lambda_c + options.noise_guard_nm) & ...
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obj.lambda_nm < (lambda_c + options.noise_guard_nm + options.noise_window_nm);
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idx_noise = idx_noise_left | idx_noise_right;
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else
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% fallback: global maximum (unsafe for pathological ASE cases)
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[~, imax] = max(psd);
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lambda_c = obj.lambda_nm(imax);
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% ASE from outer quarters of spectrum
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N = numel(obj.lambda_nm);
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idx_noise = false(size(obj.lambda_nm));
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idx_noise([3:round(N/4), round(3*N/4):N-1]) = true;
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end
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% --- extract signal window ---
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idx_signal = obj.lambda_nm > (lambda_c - options.bw_signal_nm/2) & ...
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obj.lambda_nm < (lambda_c + options.bw_signal_nm/2);
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if ~any(idx_signal)
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idx_signal(imax) = true;
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end
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cc_lambda = obj.lambda_nm(idx_signal);
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cc_psd = psd(idx_signal);
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% --- estimate ASE from local noise (flat ASE assumption) ---
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noise_lambda = obj.lambda_nm(idx_noise);
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noise_psd = psd(idx_noise);
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ase_psd = interp1(noise_lambda, noise_psd, cc_lambda, ...
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'linear', 'extrap');
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% --- convert to linear (mW / RBW) ---
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sig_lin = 10.^(cc_psd/10);
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ase_lin = 10.^(ase_psd/10);
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% --- integrate (RBW cancels) ---
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P_sig_lin = sum(sig_lin);
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P_ase_lin = sum(ase_lin);
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P_sig_dB = 10*log10(P_sig_lin);
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P_ase_dB = 10*log10(P_ase_lin);
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osnr.p_sig_db = P_sig_dB;
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osnr.p_ase_db = P_ase_dB;
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% --- OSNR direct from peak value to the noise estimate out of band ---
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osnr.direct_dB = psd(imax) - 10*log10(mean(ase_lin)) ;
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% --- OSNR in measurement bandwidth ---
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osnr.measured_dB = P_sig_dB - P_ase_dB;
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% --- normalize to reference bandwidth (usually 0.1 nm) ---
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osnr.ref_dB = osnr.measured_dB + ...
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10*log10(options.bw_signal_nm / options.ref_bw_nm);
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% --- ASE-corrected OSNR (optional definition) ---
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osnr.corrected_dB = ...
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10*log10(10^(P_sig_dB/10) - 10^(P_ase_dB/10)) - P_ase_dB;
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osnr.corrected_ref_dB = osnr.corrected_dB + ...
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10*log10(options.bw_signal_nm / options.ref_bw_nm);
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% metadata
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osnr.lambda_c_nm = lambda_c;
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osnr.bw_signal_nm = options.bw_signal_nm;
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osnr.ref_bw_nm = options.ref_bw_nm;
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if options.debugplots
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figure(100)
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xline(lambda_c,'LineWidth',2,'DisplayName','Max. OSA Value','Color',[0.8,0.8,0.8])
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obj.plot("DisplayName",'OSNR','FigureNumber',100);
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yline(osnr.p_ase_db,'LineWidth',2,'DisplayName','Signal Estimation');
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yline(osnr.p_sig_db,'LineWidth',2,'DisplayName','Noise Estimation');
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scatter(obj.lambda_nm(idx_noise),obj.psd_dBm(idx_noise),'Marker','.','LineWidth',4,'DisplayName','Noise Samples','MarkerEdgeColor','red');
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scatter(obj.lambda_nm(idx_signal),obj.psd_dBm(idx_signal),'Marker','.','LineWidth',4,'DisplayName','Signal Samples','MarkerEdgeColor','green');
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scatter(obj.lambda_nm(idx_signal),ase_psd,'Marker','.','LineWidth',4,'DisplayName','Signal Samples','MarkerEdgeColor','magenta');
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ylim([min(obj.psd_dBm), max([obj.psd_dBm,osnr.p_sig_db+5])]);
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figure(101);hold on
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xline(lambda_c,'LineWidth',2,'DisplayName','Max. OSA Value','Color',[0.8,0.8,0.8])
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xline(lambda_c - options.bw_signal_nm/2,'LineWidth',2,'DisplayName','CW - 0.5 BW','Color',[0.6,0.6,0.8])
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xline(lambda_c + options.bw_signal_nm/2,'LineWidth',2,'DisplayName','CW + 0.5 BW','Color',[0.6,0.8,0.8])
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obj.plot("DisplayName",'OSNR','FigureNumber',101);
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yline(osnr.p_ase_db,'LineWidth',2,'DisplayName','Signal Estimation');
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yline(osnr.p_sig_db,'LineWidth',2,'DisplayName','Noise Estimation');
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scatter(obj.lambda_nm(idx_signal),obj.psd_dBm(idx_signal),'Marker','.','LineWidth',4,'DisplayName','Signal Samples','MarkerEdgeColor','green');
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scatter(obj.lambda_nm(idx_signal),ase_psd,'Marker','.','LineWidth',4,'DisplayName','Signal Samples','MarkerEdgeColor','magenta');
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xlim([lambda_c - options.bw_signal_nm, lambda_c + options.bw_signal_nm])
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ylim([min(obj.psd_dBm), max([obj.psd_dBm,osnr.p_sig_db+5])]);
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end
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end
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end
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methods (Access = protected)
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function v = connect(obj)
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v = visadev(obj.visaAddress);
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end
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end
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end
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